Segmented metal bitlines

ABSTRACT

An array of memory cells of an integrated circuit are organized so metal bitlines are segmented. The memory cells may be nonvolatile memory cells such as floating gate, Flash, EEPROM, and EPROM cells. The bitlines for the memory cells are strapped to metal, and the metal bitline is segmented. The individual segments may be selectively connected to voltages as desired to allow configuring (e.g., programming) or reading of the memory cells. The programming voltage may be a high voltage, above the VCC of the integrated circuit. By dividing the metal bitlines into segments, this reduces noise between bitlines and improve the performance and reliability, and reduce power consumption because the parasitic capacitances are reduced compared to a long metal bitline (i.e., where all the segments are connected together and operated as one).

BACKGROUND OF THE INVENTION

The present invention relates to nonvolatile erasable programmablememories and more specifically, techniques for organizing or laying outthe memory cells on the integrated circuit.

Memory and storage is one of the key technology areas that is enablingthe growth in the information age. With the rapid growth in theInternet, World Wide Web (WWW), wireless phones, personal digitalassistants (PDAs), digital cameras, digital camcorders, digital musicplayers, computers, networks, and more, there is continually a need forbetter memory and storage technology. A particular type of memory isnonvolatile memory. A nonvolatile memory retains its memory or storedstate even when power is removed. Some types of nonvolatile erasableprogrammable memories include as Flash, EEPROM, EPROM, MRAM, FRAM,ferroelectric, and magnetic memories. Some nonvolatile storage productsinclude CompactFlash (CF) cards, MultiMedia cards (MMC), Flash PC cards(e.g., ATA Flash cards), SmartMedia cards, and memory sticks.

A widely used type of semiconductor memory storage cell is the Flashmemory cell or floating gate memory cell. There are other types ofmemory-cell technologies such as those mentioned above. Flash andfloating gate memory cells are discussed as merely an example. Thediscussion in this application would also apply to other memorytechnologies other than Flash and floating gate technology with theappropriate modifications. The memory cells are configured or programmedto a desired configured state. In particular, electric charge is placedon or removed from the floating gate of a Flash memory cell to put thecell into two or more stored states. One state is a programmed state andanother state is an erased state. A Flash memory cell can be used torepresent at least two binary states, a 0 or a 1. A Flash memory cellcan also store more than two binary states, such as a 00, 01, 10, or 11;this cell can store multiple states and may be referred to as amultistate memory cell, a multilevel, or multibit memory cell. Thisallows the manufacture of higher density memories without increasing thenumber of memory cells since each memory cell can represent more than asingle bit. The cell may have more than one programmed state. Forexample, for a memory cell capable of representing two bits, there willbe four programmed states.

Despite the success of nonvolatile memories, there also continues to bea need to improve the technology. It is desirable to improve thedensity, speed, durability, and reliability of these memories. It isalso desirable to reduce power consumption and reduce the cost per bitof storage.

As can be appreciated, there is a need for improving the performance andreducing the power consumption of nonvolatile memories. In particular,by.arranging and laying out the memory cells of an integrated circuit sobitlines of the memory cells are segmented, this will reduce noisebetween bitlines and improve the performance and reliability, and reducepower consumption.

SUMMARY OF THE INVENTION

The invention provides an organization for memory cells of an integratedcircuit where metal bitlines are segments. In a specific embodiment, thememory cells are nonvolatile memory cells such as floating gate, Flash,EEPROM, and EPROM cells. The bitlines for the memory cells are strappedto metal (e.g., metal-2) and this metal is segmented. The individualsegments may be selectively connected to voltages as desired to allowconfiguring (e.g., programming) or reading of the memory cells. Bydividing the metal bitlines into segments, this reduces noise betweenbitlines and improve the performance and reliability, and reduce powerconsumption because the parasitic capacitances to be charged ordischarged are reduced compared to a long metal bitline (i.e., where allthe segments are connected together and operated as one). Between thesegments are at least two pass gates (e.g., three pass gates). One passgate connects or disconnects two segments together. For each of thesegments, there is a pass gate the connects or disconnects the segmentto a supply line. The supply line will be selectively connected to avoltage such as VPP or VSS (ground).

Although the invention has been described with respect to metalbitlines, the invention may also be applied to other metal lines, suchas metal wordlines, to obtain similar benefits for those lines. However,the invention, is particularly effective for metal bitlines because thebitlines are raised to a VPP (e.g., 6.5 volts) for programming. Andswitching from 0 volts to VPP is a significant enough swing that muchnoise is generated during the switch and dynamic power is consumed.

In an embodiment, the invention is an integrated circuit including anarray of nonvolatile memory cells, wherein the array includes a metalbit line divided into a first segment and a second segment. In.particular, the metal bit line is connected or strapped to the bit linenode of a column of memory cells in the array. A first pass gate isconnected between the first and second.segment. A second pass gate isconnected between the.first segment and a supply line. For example, thesupply line may be VPP or VSS. In one implementation, the first andsecond pass gates are NMOS transistors. In another implementation, thefirst and second pass gates are CMOS pass gates.

In operation, the supply line is selectively connected to VPP or VSS,where VPP is a programming voltage level above a VCC level for theintegrated circuit. VSS is ground. The invention may further include athird pass gate connected between a VPP line and the first supply line,and a fourth pass gate coupled between a VSS line and the first supplyline. In a first mode of operation, the first pass gate is on and thesecond pass gate is off. In a second mode of operation, the first passgate is off and the second pass gate is on.

Furthermore, the memory cells may be floating gate memory cells, whichinclude Flash, EEPROM, or EPROM memory cells. The memory cells may bemultistate memory cells. Each memory cell is capable of storing aplurality of binary bits of data.

In another embodiment, each segment can have its own dedicatedconnection to VSS and VPP. Specifically, a second pass gate is connectedbetween the first segment and a first supply line. And, a third passgate is connected between the second segment and a second supply line.For example, the fast supply line may be VPP, and the second supplyline.may be VSS, or vice versa. In one implementation, the first,second, and third pass gates are NMOS transistors. In anotherimplementation, the first, second, and third pass gates are CMOS passgates.

In operation, the first supply line is selectively connected to VPP orVSS, where VPP is a programming voltage level above a VCC level for theintegrated circuit. The second. supply line is selectively connected toVPP or VSS, wherein VPP is a voltage level above a VCC level for theintegrated circuit. VSS is ground. The invention may further include afourth pass gate connected between a VPP line and the first supply line,and a fifth pass gate coupled. between a VSS line and the first supplyline.

In a first mode of operation, the first pass gate is on and the secondand third pass gates are off. In a second mode of operation, the firstpass gate is off and the second pass gate is on. Further in the secondmode of operation, the third pass gate is off.

Other objects, features, and advantages of the present invention willbecome apparent upon consideration of the following detailed descriptionand the accompanying drawings, in which like reference designationsrepresent like features throughout the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 generally shows an electronic system which various aspects of thepresent invention may be incorporated.

FIG. 2 shows an array of memory cells with wordlines and bitlines.

FIG. 3 shows a more detailed diagram of some nonvolatile memory cellsconnected to a single bitline.

FIG. 4 shows an array of memory cells where the metal layer connected tothe bitlines is segmented.

FIG. 5 shows a more detailed diagram of one segmented metal bitline andmemory cells.

FIG. 6 shows another embodiment of an array of memory cells where themetal layer connected to the.bitlines is segmented.

FIG. 7 shows a more detailed diagram of one segmented metal bitline andmemory cells of FIG. 6.

DETAILED DESCRIPTION

FIG. 1 generally shows an electronic system, such as a computer system,in which various aspects of the present invention may be incorporated.Some examples of electronics systems include computers, laptopcomputers, handheld computers, palmtop computers, personal digitalassistants (PDA), MP3 and other audio players, digital cameras, videocameras, electronic game machines, wireless and wired telephony devices,answering machines, voice recorders, and network routers. Thiselectronic system architecture includes a processor or microprocessor 21connected to a system bus 23, along with random access, main systemmemory 25, and at least one or more input-output devices 27, such as akeyboard, monitor, modem, and the like. Another main computer systemcomponent that is connected to a typical computer system bus 23 is anamount of long-term, nonvolatile memory 29. In contrast to volatilememory such as DRAM (dynamic RAM) or SRAM (static RAM), nonvolatilememory retains its stored state even after power is removed from thedevice. Typically, such a memory is a disk drive using magnetic oroptical technology with a capacity of megabytes, gigabytes, or terabytesof data storage. This data is retrieved into the system volatile memory25 for use in current processing, and can be easily supplemented,changed, or altered.

One aspect of the invention is the substitution of a specific type ofsemiconductor memory system for the disk drive but without having tosacrifice nonvolatility, ease of erasing and rewriting data into thememory, speed of access, low cost and reliability. This is accomplishedby employing an array of electrically erasable programmable read onlymemories (e.g., EEPROMs) integrated circuit chips. This type of memoryhas additional advantages of requiring less power to operate, and ofbeing lighter in weight than a hard-disk drive magnetic media memory,thus being especially suited for battery-operated portable computers.Such nonvolatile semiconductor memories include Flash disk drives,CompactFlash (TM) cards, SmartMedia (TM) cards, personal tags (P-Tag),multimedia cards, secure digital (SD) cards, and Memory sticks (R).

The bulk storage memory 29 is constructed of a memory controller 31,connected to the computer system bus 23, and an array 33 of Flash orEEPROM integrated circuit chips. Data and instructions are communicatedfrom the controller 31 to the Flash or EEPROM array 33 primarily over adata line 35. Similarly, data and status signals are communicated fromthe Flash or EEPROM 33 to the controller 31 over data lines 37. Datalines 35 and 37 may be serial or parallel, depending on theimplementation. Other control and status circuits between the controller31 and the EEPROM array 33 are not shown in FIG. 1. Furthermore, thecontroller and memory may be on separate integrated circuits or a memoryintegrated circuit may incorporate the controller. The memory may resideon separate integrated circuits. For example, multiple memory integratedcircuits may in combined to obtain the desired memory size.

Further discussion of Flash EEPROM systems and nonvolatile cells andstorage is discussed in U.S. Pat. No. 5,602,987, U.S. Pat. No.5,095,344, U.S. Pat. No. 5,270,979, U.S. Pat. No. 5,380,672, U.S. Pat.No. 5,712,180, U.S. Pat. No. 5,991,517, U.S. Pat. No. 6,222,762, andU.S. Pat. No. 6,230,233, which are incorporated by reference along withall references cited in this application.

FIG. 2 shows an array of memory cells 103 a memory integrated circuit(or chip). In an embodiment, this array is part of the Flash memory 33of FIG. 1. There may be multiple arrays of memory cells on a singlechip. The integrated circuit may be a memory such as a Flash chip or maybe another type of integrated circuit with an embedded memory portion,such as an ASIC or microprocessor with on-chip memory. The memory cellsstore binary information. In a specific embodiment, the memory cells arenonvolatile memory cells. Examples of some nonvolatile memory cells arefloating gate cells (Flash, EEPROM, or EPROM cells), phase-change cells,ferroelectric cells (FRAM), magnetic cells (MRAM), and others. Thememory cells are arranged in an array of rows and columns. There may beany number of rows and columns. The memory cells are accessed using rowsof the array.

Rows of memory cells 108 are connected to wordlines or row lines of thememory cells. Columns of memory cells 112 are connected to bitlines orcolumn lines of the memory cells. For operation of the memory cells, thewordlines and bitlines are connected to appropriate voltages in order toperform a desired operation on the memory cell or cells. For example,for configuration of the memory cells, such as erase or program, thewordlines and bitlines are connected to appropriate voltages in order toconfigure the memory cell to the desired state. These voltages aretypically high voltages, voltages at levels above the VCC (or VDD) levelof the chip. The high voltage levels for programming may be referred toas a VPP voltage. For example, voltage pumps 117 may be connected to thebitlines of the integrated circuit. And for some operations, thebitlines may need to connected to ground or VSS.

FIG. 2 also shows an area 133. Area 133 is an area outside the array 103of memory cells, but still within the same integrated circuit. Forexample, outside the memory array are the voltage pumps 1 17 and othercircuitry used in the operation of the memory integrated circuit.Examples of such circuitry in area 133 include charge pumps, senseamplifier, programming circuitry, erase circuitry, decoders, pads, inputbuffers, output buffers, logic, reference voltage generators, andothers.

In a specific embodiment, the memory cells are multistate cells, capableof storing multiple bits of data per cell. Multistate memory cells maystore two or more bits of data, such as three, four, and more. Cellscapable of storing multiple bits of data per cell may also sometimes bereferred to as multibit or multilevel cells. Details of some specificimplementations of a multistate memory cell are discussed in U.S. patent5,991,517, which is incorporated by reference. The principles of theinvention would also apply to these types of multistate memory cells.

FIG. 3 shows a more detailed diagram of one bitline 204 of memory cells.On one bitline there are a number memory cells 208. Each memory cell hasa select transistor 21 1 and a nonvolatile memory cell transistor 215.The select transistor may sometimes be referred to as a read transistor.A gate electrode for each select transistor of the bitline is connectedto a different wordline. So, for bitline 204, the select transistors areconnected to bitlines WLl to WLx, where x is an integer. In anembodiment, transistor 215 may be a floating gate transistor such as aFlash cell as discussed above. Gate of the floating transistors may bereferred to as a control gate or erase gate electrode and are connectedtogether. The memory cells shown in FIG. 3 and elsewhere in thisapplication are shown merely as an example, and the invention alsoapplies to other types of memory cells. For example, the memory cellsmay be MRAM, FRAM, or phase-change devices. And, the invention may alsobe applied to volatile memory cells such as DRAM and SRAM cells.

The bitlines are generally connected using diffusion. In the case wherethe select transistor is an NMOS or n-channel transistor, the diffusionis n+diffusion. In order to minimize resistance, this bitline isstrapped (connected) to an upper layer metal or other conductor withless resistance than diffusion. A specific embodiment discussed in thisapplication has a bitline strapped in a second-layer metal, metal-2.However, it is understood that for a given integrated circuit processthere are typically many different layers of metal, and a given processmay have two or more layers of metal. The invention would applysimilarly to bitlines run and connected to metal or other electricallyconductive layers other than metal-2. For example, the bitline of theinvention may be run in any metal or conductive layer such as metal-1,metal-2, metal-3, metal- 4, metal-5, metal-6, or others.

In a specific embodiment, the bitline is strapped to metal-2(second-layer metal) using a metal- 1 (first-layer metal, below thesecond-layer metal) jumper. In this approach, the bitlines of FIGS. 2and 3 are run in metal-2 and the wordlines are run in metal- 1. Thewordlines and bitlines are generally not run in the same metal layersince this would mean the metal wordlines and bitlines would short eachother out. In an alternative embodiment, the bitlines and wordlines arerun in metal-l and metal-2, respectively.

Each of the bitlines (array lines) have parasitic capacitance to ground(e.g., parasitic capacitance 122 of FIG. 2). FIG. 3 does not showparasitic capacitances to ground in order to simplify the diagram, butis shown in FIG. 2. Further, there is parasitic capacitance.not only toground, but between the bitlines themselves as well (e.g., parasiticcapacitances 125 and 128). These parasitic capacitances are distributedcapacitances, distributed on the bitline.

Although not a DC component, charging and discharging the bitlinestranslate into a large current, especially for massive parallel (reador) programming, when speed (performance) is an important factor. As anexample, although the bitline parasitic capacitance may be about 1picofarads to 3 picofarads, charging 2000 bitlines during programnming,at a VPP level of about 6.5 volts in about 0.5 microseconds translatesinto about 25 milliamps to 80 milliamps of VPP current. This couldtranslate into about 100 milliamps to about 250 milliamps of IDD currenttotal. This is a significant amount of dynamic power consumption. Thiscan be a serious limitation to the number of cells that can be processedin parallel, and thus to the performance.

FIG. 4 shows another organization for an array memory cells. The metal(e.g., metal-2) bits lines are broken into a number of segments, such as304 and 308. In a specific example, the array of memory cells is dividedinto eight portions and there are seven metal bitlines portions. At anend of the array is circuitry 31 1 to be connected to the bitlines.These are connected or disconnected to the bitlines using pass gates315.

Between metal bitline segments is circuitry 322. In an embodiment, thiscircuitry is present between every other metal bitline segment. Thecircuitry for one bitline includes three transistors. A pass transistoror pass gate 328 which can connect segments 304 and 308 together. Thereis a pass transistor 333 which can connect or disconnect segment 304 toa line 337. There is a pass transistor 343 which can connect ordisconnect segment 308 to a line 347. The pass transistors shown areNMOS transistors. However, there are many implementation of passtransistors that may.be used, and combinations of these. For example,the pass transistors may be a CMOS pass gate, where NMOS and PMOStransistors are connected in parallel.

When the gate of the pass transistors is asserted (such as connected theVCC), the pass transistors connects its source and drains nodes by avery low resistance path. This may be referred to as turning a pass gateon or an ON pass gate. For example, when the gate of transistor 328 isconnected to VDD, segments 304 and 308 are effectively connectedtogether. Similarly, when the gate of transistor 333 is connected toVDD, segment 304 is effectively connected to line 337. And, when thegate of transistor 343 is connected to VDD, segment 308 is effectivelyconnected to line 347. When the pass gates are connected to ground, theydisconnect the source and drain nodes. This may be referred to asturning a pass gate off or an OFF pass gate.

Another approach which may be used is to use high voltage pass gates,where a voltage higher than VCC is connected to the gate of the passgate. This will lower the resistance or impedance between the source anddrain.

Figure-5 shows a more detailed diagram of metal segments 304 and 308 andthe circuitry between the segments. In this figure, the gate or controlelectrode of transistor 328 is referred to as the VPG node. Bitlines formemory cells of wordlines .WLl to WvLn are connected to metal segment304. Bitlines for memory cells of wordlines VWLn+1 to WLm are connectedto metal segment 308. In the case the memory cells are evenly divided, mwill be equal to 2*n since there will be an equal number of memory cellsfor each segment. A metal bitline segmentation includes three passtransistors, one acting as a (serial) cornect or disconnect device to adata node, and the others as local paths to ground or a voltage source,either VPP or a stop voltage (e.g, VSS). This present combination alsoacts as a Y selection. Some modes of operation for the segmented memoryarray architecture are summarized in the following table A. TABLE A PassGate 333 Pass Gate 328 Pass Gate 343 Mode A OFF ON OFF Mode B ON OFF OFFMode C OFF OFF ON

When an entire portion of an array of memory cells is in mode A, theindividual segments of the array are connected together. Then the.arraymay be operated similarly as the array shown in FIG. 2. In mode B,segment 304 is connected line 333. This segment may be connected to VPPthrough a pass gate 405 or connected to VSS through a pass gate 407,depending on the desired operation. In mode C, segment 308 is connectedto line 347. This segment may be connected to VPP through a pass gate415 or connected to VSS through a pass gate 417, depending on thedesired operation. In an embodiment, pass gates 405,407,415, and 417 areformed outside (such as in area 133 of FIG. 2) of the array of memorycells and outputs, lines 334 and 347 are fed into the array. Thisconfiguration allows maximal packing of the memory cells. In analternative embodiment, pass gates 405, 407, 415, and 417 are embeddedwithin the array of memory cells.

By splitting the metal bitline into a number of segments andconveniently connecting or isolating them, the high AC current duringprogramming or read is accordingly reduced. This is because the lengthof a metal segment is much shorter than the entire metal segment (suchas in FIG. 2). There is less parasitic capacitance for a shortersegment, and thus the performance when doing parallel read orprogramming improves and the dynamic power consumption goes down.

FIG. 6 shows another organization for an array memory cells. Thisorganization is similar to that in FIG. 4, but the circuitry between thesegments of the memory is allocated differently. However, the operationof the circuitry will be similar. The metal (e.g., metal-2) bits linesare broken into a number of segments, such as 304 and 308. In a specificexample, the array of memory cells is divided into eight portions andthere are seven metal bitlines portions. At an end of the array iscircuitry 311 to be connected to the bitlines. These are connected ordisconnected to the bitlines using pass gates 315.

Between each metal bitline segment is circuitry 321. Circuitry 323 issimilar circuitry to circuitry 321 in an adjacent location betweensegments. In portion 321, the circuitry for one bitline includes twotransistors. A pass transistor or pass gate 328 which can connectsegments 304 and 308 together. There is a pass transistor 333 which canconnect or disconnect segment 304 to a line 337. In portion 323, thereis a pass transistor 343 which can connect or disconnect segment 308 toa line 347. The pass transistors shown are NMOS transistors. However,there are many implementation of pass transistors that may be used, andcombinations of these. For example, the pass transistors may be a CMOSpass gate, where NMOS and PMOS transistors are connected in parallel.

When the gate of the pass transistors is asserted (such as connected theVCC), the pass transistors connects its source and drains nodes by avery low resistance path. This may be referred to as turning a pass gateon or an ON pass gate. For example, when the gate of transistor 328 isconnected to VDD, segments 304 and 308 are effectively connectedtogether. Similarly, when the gate of transistor 333 is connected toVDD, segment 304 is effectively connected to line 337. And, when thegate of transistor 343 is connected to VDD, segment 308 is effectivelyconnected to line 347. When the pass gates are connected to ground, theydisconnect the source 4nd drain nodes. This may be referred to asturning a pass gate off or an OFF pass gate.

Another approach which may be used is to use high voltage pass gates,where a voltage higher than VCC is connected to the gate of the passgate. This will lower the resistance or impedance between the source anddrain.

FIG. 7 shows a more detailed diagram of metal segments 304 and 308 ofFIG. 6 and the circuitry between the segments. In this figure, the gateor control electrode of transistor 328 is referred to as the VPG node.Bitlines for memory cells of wordlines WL1 to WLn are connected to metalsegment 304. Bitlines for memory cells of wordlines WLn+l to WLm areconnected to metal segment 308. In the. case when the memory cells areevenly divided, m will be equal to 2*n since there will be an equalnumber of memory cells for each segment. A metal bitline segmentationincludes two pass transistors, one acting as a (serial) connect ordisconnect 15 device to a data node, and the other as a local path toground or a voltage source, either a stop voltage (e.g., VSS) or VPP,respectively. This present combination also acts as a Y selection. Somemodes of operation for the segmented memory array architecture aresummarized in the table B below. TABLE B Pass Gate 333 Pass Gate 328Mode A OFF ON Mode B ON OFF Mode C OFF OFF

When an entire portion of an array of memory cells is in mode A, theindividual segments of the array are connected together. Then the arraymay be operated similarly as the array shown in FIG. 2. In mode B,segment 304 is connected line 333. This segment may be connected to VPPthrough a pass gate 405 or connected to VSS through a pass gate 407,depending on the desired operation. In mode C, one or more segments iscompletely disconnected from either neighboring segments or VSS or VPP,or combinations of these. Segment 308 is floating when gate 343 and 328are off. This removes the capacitance and parasitic capacitance ofsegment 308 from the rest of the array, and may be used to improve theperformance when operating on another segment of the array. In anembodiment, pass gates 405, 407, 415, and 417 are formed outside (suchas in area 133 of FIG. 2) of the array of memory cells and outputs,lines 334 and 347 are fed into the array. This configuration allowsmaximal packing of the memory cells. In an alternative embodiment, passgates 405, 407, 415, and 417 are embedded within the array of memorycells.

By splitting the metal bitline into a number of segments andconveniently connecting or isolating them, the high AC current duringprogramming or read is accordingly reduced. This is because the lengthof a metal segment is much shorter than the entire metal segment (suchas in FIG. 2). There is less parasitic capacitance for a shortersegment, and thus the performance when doing parallel read orprogramming improves and the dynamic power consumption goes down.

This description of the invention has been presented for the purposes ofillustration and description. It is not intended to be exhaustive or tolimit the invention to the precise form described, and manymodifications and variations are possible in light of the teachingabove. The embodiments were chosen and described in order to bestexplain the principles of the invention and its practical applications.This description will enable others skilled in the art to best utilizeand practice the invention in various embodiments and with variousmodifications as are suited to a particular use. The scope of theinvention is defined by the following claims.

1. An integrated circuit comprising: an array of nonvolatile memorycells, wherein the array comprises a metal bit line divided into a firstsegment and a second segment; a first pass gate coupled between thefirst and second segment; a second pass gate coupled between the firstsegment and a first supply line; and a third pass gate coupled betweenthe second segment and a second supply line.
 2. An integrated circuitcomprising: an array of nonvolatile memory cells, wherein the arraycomprises a metal bit line divided into a first segment and a secondsegment; a first pass gate coupled between the first and second segment;and a second pass gate coupled between the first segment and a firstsupply line.
 3. The integrated circuit of claim 1 wherein the memorycells are floating gate, Flash, EEPROM, or EPROM memory cells.
 4. Theintegrated circuit of claim 1 wherein the memory cells are multistatememory cells.
 5. The integrated circuit of claim 1 wherein each memorycell is capable of storing a plurality of binary bits of data.
 6. Theintegrated circuit of claim 1 wherein the first, second, and third passgates are NMOS transistors.
 7. The integrated circuit of claim 2 whereinthe first and second pass gates are NMOS devices.
 8. The integratedcircuit of claim 1 wherein the first, second, and third pass gates areCMOS pass gates.
 9. The integrated circuit of claim 2 wherein the firstsupply line is selectively coupled to VPP or VSS, wherein VPP is avoltage level above a VCC level for the integrated circuit.
 10. Theintegrated circuit of claim 1 wherein the second supply line isselectively coupled to VPP or VSS, wherein VPP is a voltage level abovea VCC level for the integrated circuit.
 11. The integrated circuit ofclaim 1 further comprising: a fourth pass gate coupled between a VPPline and the first supply line; and a fifth pass gate coupled between aVSS line and the first supply line.
 12. The integrated circuit of claim2 further comprising: a third pass gate coupled between a VPP line andthe first supply line; and a fourth pass gate coupled between a VSS lineand the first supply line.
 13. The integrated circuit of claim 1 1wherein the VPP line is at or above a VCC supply voltage for theintegrated circuit.
 14. The integrated circuit of claim 1 wherein in afirst mode of operation, the first pass gate is on and the second andthird pass gates are off.
 15. The integrated circuit of claim 1 whereinin a second mode of operation, the first pass gate is off and the secondpass gate is, on.
 16. The integrated circuit of claim 15 wherein thethird pass gate is off.
 17. The integrated circuit of claim I whereinthe second and third pass gates are outside the array.
 18. Theintegrated circuit of claim I wherein the first pass gate is within thearray of nonvolatile cells.
 19. The integrated circuit of claim 1wherein the first pass gate is within the array of nonvolatile cells,and the second and third pass gates are outside the array of nonvolatilecells.
 20. The integrated circuit of claim 2 wherein both pass gates areoff in a mode of operation.